CN1559108A - Method and device for an ultra-wideband communication system with multiple detectors - Google Patents

Abstract

A method and apparatus for detecting ultra wide-band (UWB) signals using multiple detectors having dynamic transfer characteristics. A receiver circuit is implemented using devices such as op-amps to provide the required dynamic characteristics. Detectors used in the UWB communication systems of the present invention utilize direct sequence spread spectrum (DSSS) technology for multiple access reception.

Description

Method and device for an ultra-wideband communication system with multiple detectors

REFERENCE FOR APPLICATION

[01] This application is related to the unapproved and assigned U.S. Patent Application No. 09/847,777, entitled "Method and Apparatus for Signal Identification in Ultra-Wideband Communications", filed on May 1, 2001 application, and hereby declares its incorporation.

Background of the Invention

[02] In recent years, ultra-wideband (UWB) communication systems have received extensive attention due to their anti-multipath capability, simple design of radio frequency modules, and low cost. UWB transmission uses very short radio pulses whose characteristic spectral lines cover a wide range of radio frequencies. Therefore, the generated UWB signal has high bandwidth and frequency diversity. Such features make them ideal for a variety of applications, such as high-speed wireless data communications, and low-cost home wireless networking.

[03] In commonly owned and assigned US Patent Application No. 09/847,777, a method and apparatus for authenticating signals in a UWB communication system is disclosed. According to the application, the discrimination of the signal is excellent in the unipolar transmission of the signal. However, if the required transmission signal is bipolar, or if multiple UWB transmitters are operating at the same time, as in the case of multiple users accessing an application, interference can occur between users.

Invention Summary

[04] In general, embodiments of the present invention refer to methods and apparatus for transmitting and/or discriminating ultra-wideband (UWB) signals.

[05] According to an illustrated aspect of the present invention, a UWB communication system includes one or more transmitters operable to transmit one or more UWB signals, and a receiver operable to receive the UWB signals. In this aspect of the invention, the receiver portion of the system comprises a first circuit with a first pulse generator operable to generate a first train of pulses responsive to the UWB signal; a first circuit connected in parallel with the first two circuits, the second circuit is equipped with a second pulse generator operable to generate a second pulse train in response to the UWB signal; and a pulse processing circuit operable to interpret the first and second code sequences, thereby confirming Information carried in UWB signals.

[06] In accordance with another illustrated aspect of the present invention, a receiving circuit for receiving UWB signals includes an antenna operable to receive UWB signals; a first circuit equipped with a first pulse generator configured to operable to generate a first train of pulses responsive to the UWB signal; a second circuit connected in parallel with the first circuit, the second circuit being provided with a second pulse generator operable to generate a second train of pulses responsive to the UWB signal; and a pulse processing circuit operable to interpret the first and second code sequences to identify information carried in the UWB signal.

[07] According to another aspect exemplified by the present invention, a UWB communication system includes a plurality of transmitters operable to transmit a corresponding number of UWB signals; a plurality of detectors each equipped with a pulse generator circuitry for generating a unique pulse sequence corresponding to the UWB signal; and a pulse processing circuit operable to interpret the code sequence to identify information carried in the UWB signal.

[08] Still according to another aspect exemplified by the present invention, a method for generating information contained in a UWB signal comprises receiving a UWB signal, extracting a first pulse sequence from the UWB signal, and extracting a first pulse sequence from the UWB signal A second pulse sequence is extracted from the signal, and information is extracted based on the first and second pulse sequences.

[09] A further understanding of the present invention may now be obtained having regard to the features and advantages of the present disclosure and by reference to the detailed description given in the remainder of the specification and accompanying drawings.

A brief description of the drawings

[10] FIG. 1A shows a block diagram of a transmitter for a UWB communication system according to an embodiment of the present invention.

[11] FIG. 1B shows a block diagram of a receiver for a UWB communication system according to an embodiment of the present invention.

[12] Figure 2A shows a digital "0" represented by a positive Gaussian periodic waveform.

[13] Figure 2B shows a digital "1" represented by a negative Gaussian periodic waveform.

[14] FIG. 3 shows an i-v conversion characteristic of a nonlinear circuit element used in a discrimination circuit of a receiver according to an embodiment of the present invention.

[15] Figure 4 shows a UWB receiver circuit with an op-amp based circuit that can provide i-v conversion characteristics similar to those shown in Figure 3.

[16]] Fig. 5 shows a receiver circuit of a UWB system according to an embodiment of the present invention.

[17] Figure 6 illustrates a response of the receiver shown in Figure 5, based on numerical simulations; and

[18] FIG. 7 illustrates a receiver circuit with four detectors in a UWB communication system according to an embodiment of the present invention.

Detailed description of the invention

[19] In US Patent Application No. 09/847,777, a UWB receiver equipped with a detector with an N-type i-v characteristic curve is disclosed. In this application, multiple detectors are used similar to those proposed in Patent Application No. 09/847,777, and a spread spectrum quadrature modulation scheme is used in the UWB transmission system, so that Multiple UWB transmitters can operate simultaneously in the system.

[20] FIG. 1 shows a block diagram of a UWB communication system according to an embodiment of the present invention. The communication system includes one or more transmitters 5 and receivers 7, as shown in Figures 1A and 1B, respectively. Although only one transmitter 5 and one receiver 7 are shown in Fig. 1, multiple communication channels are also included in the embodiment of the present invention, so that two or more transmitters 5 operate simultaneously on the same frequency channel, and are communicated by both One or more receivers 7 receive.

[21] In order to realize multi-channel communication, spread spectrum technique is used to overcome the interference relationship. In the embodiments mentioned here, the particular spread spectrum technique used is called "Direct Sequence" Spread Spectrum (DSSS) technique. In a typical DSSS transmitter, a pseudo-random or pseudo-noise (PN) code sequence generator is used, which connects a modulator to the transmitter to propagate the transmitted signal. A PN code sequence contains a code sequence composed of '1' and '0', and its correlation is similar to that of white noise. A PN code generator 12 is included as part of the transmitter 5, as shown in FIG. 1A. PN code generator 12 provides a pseudorandom code sequence. This pseudo-random code sequence is modulated into a message signal provided by an information source 10 . The message signal contains a large number of data symbols for transmission. The modulated signal is output from the modulator 11 and then processed by the waveform controller so that the modulated signal meets the requirements before being transmitted by the antenna 14 .

[22] There are also different PN code sequence schemes. The PN sequences that are widely used include the longest shift register sequence (or m-sequence for short), Gaud sequence and Kasami sequence. In one embodiment of the invention, modulator 11 uses an M-ary (approximately) quadrature modulation (OM) scheme with a symbol table

${\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; \&Element;</span><span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>}_{\mathrm{<span\; class="notranslate">\; j</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}^{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>$

in

${\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}^{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; )</span>$

is the jth symbol, and the parameter N _s is the PN sequence $c=(c_0,{\mathrm{<figure-callout\; id="1"\; label="c"\; filenames="A0281871600241.png,A0281871600261.png"\; state="\{\{state\}\}">c</figure-callout>}}_1,..c_{N_{\mathrm{the\; s}}-1})$ The period of , which is generated from the PN code generator 12, c _j ^k is the k-th segment of the j-th cyclic shift of c, $c_j^k\&Element;\left\{\mathrm{0,1}\right\}$ , and T _f is the duration of the segment. The character table size here satisfies M=2 ^I <N _s , where I is an integer.

[23] The modulator 11 also includes a pulse generator which generates an analog waveform p(t) with a pulse time _Tp . In order to ensure that there is no mutual interference between segments and symbols, the segment duration T _f satisfies the condition T _p + T _d < T _f , where T _d is the propagation delay of the channel.

[24] In the following discussion, the digital "0" is represented by a Gaussian single-cycle waveform, as shown in Fig. 2A. The mathematical description of a Gaussian monocyclic signal is as follows: $p\left(t\right)=V_0{e}^{{(-\frac{t}{\mathrm{\&tau;}})}^2},$ where _V0 is the maximum amplitude and τ is a time constant.

[25] The digital "1" is represented by sending a negative Gaussian single-cycle waveform, as shown in Figure 2B. It can be recorded by other types of epipolar waveforms, for example, a second derived Gaussian pulse can also be used.

[26] The modulation scheme discussed here actually uses epipolar signals at the segment level. This point, and the characteristics of the PN sequence, together make the interference between any two symbols in the X column close to zero when the period N _s of the PN sequence is very long. Therefore, this signaling scheme is called a quadrature modulation.

[27] FIG. 1B shows a block diagram of a receiver 7 according to an embodiment of the present invention. The received UWB RF signal 120 will first pass through an optional waveform control circuit, such as a filter, integrator or packet detector, to help optimize discrimination.

[28] Signal 101, which represents the received conditioned UWB RF signal, is connected to parallel circuits 109 and 110. Circuit 109 comprises an inductor 103 and a circuit 104 connected in series to inductor 103 . Circuit 104 has N-type i-v conversion characteristics, as shown in FIG. 3 . This characteristic curve can be dynamically manipulated via input 107. The output of circuit 109 consists of a series of pulses or silences, depending on the signal received. Circuit 109 can be thought of as a "positive" detector because it only generates pulses when the received signal is above a certain positive threshold.

[29] Similarly, the circuit 110 includes an inductor 105 and another circuit 106 connected in series to the inductor 105 . Similar to circuit 104, circuit 106 has N-type i-v conversion characteristics. In one embodiment of the invention, circuits 104 and 106 are non-linear circuits. Careful observation of the transfer characteristics of circuits 104 and 106 reveals that by providing a predetermined, controllable voltage at input 108, the transfer curve of circuit 106 can be positioned at different positions. Input 108 can also be used to dynamically adjust the conversion curve by providing different voltages to input 108 . The output of circuit 109 is also similar, and the output of circuit 110 contains a series of pulses or silences, depending on the signal received. Since the transfer curves of circuit 109 and circuit 110 are different, their responses to the same signal are different. Circuit 110 can be thought of as a "negative" detector because it only generates pulses when the received signal is below a certain positive threshold.

[30] The output signals of circuits 109 and 110 are fed into a pulse processing circuit 112 which confirms the digital signal 113 for correct interpretation. The pulse processing circuit may be implemented based on a logic circuit using a gate array board, a digital signal processing board, or other similar components. A further detailed description related to the signal processing circuit will be given below.

[31] Looking again at the characteristic curve of the circuit 104 shown in FIG. 3, it can be seen that its transfer curve contains two stop points p1=(V _v , _iv ) and p3=(V _p , i _p ). Here, _iv and _ip represent the current values of the valley and peak of the N-type curve, respectively. Although shown as such, the curve is not necessarily piecewise linear. All that is required is that the characteristic curve be encompassed by three distinct regions: the middle region with a negative impedance slope, which is bounded by the other two regions with positive impedance slopes. In case the input signal acts on the line segment P1-P3 of the characteristic curve, pulses will be generated along the state trajectory P4→P3→P2→P1→P4. The number of pulses generated depends on the time available (eg the period during which the input signal is applied in line segment P1-P3) and the speed of the trajectory. The basic operation of circuit 106 is similar to that of circuit 104 we discussed, except that the termination point is at a different location.

[32] Referring now to FIG. 4, it shows how the circuit 104 of the positive detector 109 shown in FIG. 1, and the circuit 106 of the negative detector 110 are realized by using an operational amplifier circuit . These operational amplifier circuits have piecewise linear i-v characteristics similar to those shown in Figure 3. In the illustrated embodiment, the slope and stop point of the characteristic curve can be easily adjusted by changing the values of R1, R2, R3, R4, R5, R6, and the bias voltages of Vcc and Vdd. The control inputs 107 and 108 in FIG. 1 are labeled 403, 404 respectively in FIG. 4 . In a particular embodiment, two different fixed bias voltages can be used and thus the conversion curve is interpreted to two different predetermined positions. In embodiments of the invention where a more sophisticated operating environment is required, the operating noise level can be monitored to determine the appropriate voltages for the control inputs 403 and 404 . In such an embodiment, the N-type characteristic curve is dynamically interpreted to different locations in real time.

[33] Figure 5 shows an alternative detector pair for a UWB receiver 50, in accordance with another illustrated embodiment of the present invention. In this UWB receiver system 50 an input signal from a signal source 501 is sent directly to a circuit 509 in the same manner as it is fed into the receiver 7 equipped with 109 in FIG. 1 . However, before being sent to circuit 510, the input signal is converted by a conversion circuit 511. The i-v conversion characteristics of circuit 510 are similar to circuit 509. Because the two detectors 509 and 510 receive signals with opposite polarities, each responds differently and generates a different pulse sequence.

[34] will now describe the UWB receiver response using the above-mentioned spread-spectrum quadrature modulation scheme, see Fig. 5. For the convenience of explanation, an M=2-element modulation scheme is assumed in the description as a simple extension to multi-level modulation. Also, in this illustrated example, a 7-segment m-sequence is used, where c={1110100}. Therefore, symbol '1' is represented as 1110100 and symbol '2' is 1101001, so symbol '2' is a variant of symbol '1' shifted by 1 bit.

[35] Figure 6 illustrates a standard response of the receiver shown in Figure 5, based on numerical simulations. Waveform 601 represents symbols to be transmitted. In this illustrated example, the transmitted signal is symbol 1 followed by symbol 2. After the DSSS method and PN sequence processing just mentioned, the modulated signal is shown as waveform 602 . Due to the presence of additional white Gaussian noise in the channel, the received signal is somewhat corrupted, as shown by waveform 603 . The output of the two circuits 509 and 510 contains a series of pulses which depend on the position of the signal and the level of noise. These outputs are shown as waveforms 604 and 605 for the negative and positive detectors in FIG. 5, respectively. Depending on the tuning of the circuit, the presence of a digital signal can generate a specific number of pulses. In this illustrated example, 4 pulses are used. Waveform 606 shows details of waveform 605 . Immediately after these pulses are received, the pulse processing system will validate the interpreted digital signal.

[36] The output signals of the circuits 509 and 510 are fed into a pulse processing circuit 512 which confirms the correct interpretation of the digital signal 113. The pulse processing circuit 512 can be implemented using a logic circuit using a gate array board, a digital signal processing board, or other similar components.

[37] The pulse processing circuit 512 completes the following tasks. First, before transmission, when the received symbol x _i (t) is fed into the positive and negative detectors in the M × N _i matrices A and B, it stores an a priori ideal pulse occurrence instant, where N _i is the number of pulses generated per symbol. The (i, j)th element of A and B marked by a(i, j) and b(i, j) is the moment when the jth pulse occurs. Second, the pulse processing circuit 512 converts the result array W=(w ₀ , w ₁ , . . . , w _M-1 ) of the positive detector 509 and the result array U=(u ₀ , u ₁ , ..., u _M-1 ) are initialized to zero. Third, the pulse processing circuit 512 stores the pulse generation instants from the detectors into the array Y=(y ₁ , y ₂ , . . . , y _N ) corresponding to the positive detector 509, and the array corresponding to the negative detector 510 in the array Z=(z ₁ , z ₂ , . . . , z _N ). Fourth, for each set of 0≤i≤M- ₁ , 1≤j≤N1 and 1≤k≤N, the pulse processing circuit 512 checks, for the positive detector 509, whether the condition a(i, j) - Δ≦y _k ≦a(i,j)+Δ. If so, the array _wi is incremented by one. The parameter Δ is the width of the detection window, and it is a pre-designed parameter. Similarly, the pulse processing circuit 512 checks, for the negative detector 510, whether the condition b(i,j)-Δ≦z _k ≦b(i,j)+Δ is satisfied. If so, the array u _i is incremented by one corresponding to the negative detector. Fifth, the pulse processing circuit 512 combines the array of positive detectors 509 and negative detectors 510 according to δ=u _i +w _i , i=0, 1, . . . , M-1. Finally, if δ _m is the largest among all δ _i , 0≤i≤M-1, the pulse processing circuit 512 determines that x _m (t) is the most suitable signal to transmit. In this example, the interpreted symbol is shown as signal 607, which is consistent with the transmitted symbol.

[37] The above is a complete description of the numerous possible embodiments involved in the present invention, as well as its various alternatives, modifications and equivalents. For example, there may be structures with multiple detectors which are included within the scope of the description of Figure 7 of this application, eg a 4 detector system with 4 N-type circuits connected in parallel. The i-v transition characteristic of each N-type circuit can be constructed so that it has a different set of termination points so that it responds to an input signal differently than other N-type circuits which also have their own set of stop points point characteristic. Figure 7 shows an example of a special 4-detector system. However, it should be understood that other embodiments having more or fewer detectors are possible in accordance with the invention described herein. For these or other reasons, the above description should not be taken as limiting the scope of the invention, which scope is defined in the appended claims.

Claims (43)

1. A receiver circuit for receiving an ultra-wideband (UWB) signal comprising: an antenna operable to receive UWB signals; a first circuit configured with a first pulse generator operable to generate a first sequence of pulses responsive to the UWB signal; a second circuit connected in parallel with the first circuit, the second circuit being provided with a second pulse generator operable to generate a second pulse train responsive to the UWB signal; and A pulse processing circuit is operable to interpret the first and second code sequences and validate information carried in the UWB signal. 2. The receiver circuit of claim 1, wherein the first and second circuits are non-linear circuits. 3. In the receiver circuit of claim 1 , wherein the first and second pulse generators each have an associated transfer curve characterized by an unstable domain bounded by a stable domain defined. 4. In the receiver circuit of claim 1, said UWB signal comprises a pseudo-random code sequence modulated within the message signal. 5. In the receiver circuit of claim 4, the modulation of the pseudo-random code sequence uses an M-ary quadrature modulation scheme. 6. In the receiver circuit of claim 4, the modulation of the pseudo-random code sequence uses an epipolar modulation scheme. 7. In the receiver circuit of claim 6, the dipole modulation scheme gives positive and negative Gaussian periodic waveforms to represent digital "0" and digital "1", respectively. 8. In the receiver circuit of claim 1, the first pulse generator generates the first pulse train only when the level of the received UWB signal is above a predetermined positive threshold. 9. In the receiver circuit of claim 8, the second pulse generator generates the second pulse train only when the level of the received UWB signal is below a predetermined negative threshold. 10. An ultra-wideband communication system, comprising: one or more transmitters operable to transmit one or more UWB signals; and A receiver operable to receive UWB signals, the receiver comprising: a first circuit configured with a first pulse generator operable to generate a first sequence of pulses responsive to the UWB signal; a second circuit connected in parallel with the first circuit, the second circuit being provided with a second pulse generator operable to generate a second pulse train responsive to the UWB signal; and A pulse processing circuit is operable to interpret the first and second code sequences and determine information carried in the UWB signal. 11. In the UWB communication system of claim 10, the first and second circuits are nonlinear circuits. 12. In the UWB communication system of claim 10, the first and second pulse generators each have an associated transfer curve characterized by an unstable domain bounded by a stable domain . 13. The UWB communication system of claim 10, wherein each of the one or more transmitters is provided with a modulator for modulating a pseudo-noise code sequence into the message signal. 14. In the UWB communication system of claim 10, the first pulse generator generates a pulse train only when the level of the received UWB signal is higher than a predetermined positive threshold. 15. In the UWB communication system of claim 10, the second pulse generator generates a pulse train only when the level of the received UWB signal is lower than a predetermined negative threshold. 16. In the UWB communication system of claim 13, each modulator uses an M-ary quadrature modulation scheme. 17. In the UWB communication system of claim 13, the modulator uses a dipolar modulation scheme. 18. In the UWB communication system of claim 17, the dipolar modulation scheme gives positive and negative Gaussian periodic waveforms to represent digital "0" and digital "1", respectively. 19. An ultra wideband (UWB) communication system comprising: a plurality of transmitters operable to transmit a corresponding plurality of UWB signals; a plurality of detectors each equipped with a pulse generating circuit for generating a unique pulse train in response to the UWB signal; and A pulse processing circuit is operable to interpret the pulse train and confirm information carried in the UWB signal. 20. In the UWB communication system of claim 19, each pulse generating circuit is a non-linear circuit. 21. The UWB communication system of claim 19, wherein the plurality of detectors are operable to generate pulse trains upon receipt of a plurality of UWB signals transmitted simultaneously. 22. In the UWB communication system of claim 19, the plurality of transmitters are configured to transmit simultaneously within the same frequency channel. 23. In the UWB communication system of claim 22, spread spectrum techniques are used to generate UWB signals. 24. In the UWB communication system of claim 23, the spread spectrum technique used is direct sequence spread spectrum technique. 25. In the UWB communication system of claim 24, each transmitter is provided with a modulator for modulating a pseudo-noise (PN) sequence to generate the UWB signal. 26. In the UWB communication system of claim 25, each modulator uses an M-ary quadrature modulation scheme. 27. In the UWB communication system of claim 25, the modulator uses a dipolar modulation scheme. 28. In the UWB communication system of claim 27, the dipolar modulation scheme gives positive and negative Gaussian periodic waveforms to represent digital "0" and digital "1", respectively. 29. A receiver circuit for receiving ultra wideband (UWB) signals, comprising: an antenna operable to receive UWB signals; a first circuit configured with a first pulse generator operable to generate a first sequence of pulses responsive to the UWB signal; a rectifier configured to receive the UWB signal and provide a rectified UWB signal; a second circuit connected in parallel with the first circuit, the second circuit being provided with a second pulse generator operable to generate a second pulse train responsive to the UWB signal; and A pulse processing circuit is operable to interpret the first and second code sequences and validate information carried in the UWB signal and the rectified UWB signal. 30. In the receiver circuit of claim 29, said first and second circuits are non-linear circuits. 31. In the receiver circuit of claim 29, the first and second pulse generators each have an associated transfer curve characterized by an unstable domain bounded by a stable domain . 32. In the receiver circuit of claim 29, said UWB signal includes a pseudorandom code sequence modulated within the message signal. 33. In the receiver circuit of claim 32, the pseudorandom code sequence is modulated using an M-ary quadrature modulation scheme. 34. In the receiver circuit of claim 29, the pseudorandom code sequence is modulated using an epipolar modulation scheme. 35. In the receiver circuit of claim 34, the dipole modulation scheme gives positive and negative Gaussian periodic waveforms to represent digital "0" and digital "1", respectively. 36. A method of generating information from an ultra wideband (UWB) signal, comprising: Receive UWB signal; generating a first pulse train from the UWB signal; generating a second pulse train from the UWB signal; and Information is generated based on the first and second pulse sequences. 37. The method of claim 36, the step of generating the first sequence of pulses includes applying the UWB signal to the first non-linear circuit and the step of generating the second sequence of pulses includes applying the UWB signal to the second non-linear circuit. 38. In the method of claim 37, the UWB signal is applied to the first and second circuits at substantially the same time. 39. In the method of claim 36, spread spectrum techniques are used to generate the UWB signal. 40. In the method of claim 39, the spread spectrum technique used is a direct sequence spread spectrum technique. 41. In the method of claim 36, the UWB signal is generated with a modulated pseudo-noise code sequence. 42. In the method of claim 41, the pseudo-noise is modulated using an M-ary quadrature modulation scheme. 43. In the method of claim 42, the pseudo-noise is modulated using an epipolar modulation scheme.

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